Metal-metal bonding

ABSTRACT

Metal to metal bonding using a heat-sensitive adhesive is effected by application of ultrasonic energy to a metal-adhesivemetal assembly. The metals bonded may be, for example, sheets, strips, or the ends of a can blank, thus producing a side-seam.

United States Patent Inventors Raymond John Ceresa;

Kenneth Martin Slnnott, both of London,

2,985,954 5/1961 Jones 29/470 3,184,354 5/1965 Strother. 156/733,193,169 7/1965 Arnold 156/73 X 3,193,424 7/1965 Scott 156/73 FOREIGNPATENTS 33-9142 1959 Japan 156/73 660,845 1963 Canada 156/73 OTHERREFERENCES Ultrasonic Assembly- Bulletin 8-888, Brunson Sonic Power Co.

Primary Examiner-Carl D. Quarforth Assistant Examiner-Brooks 1-1. HuntAttorneys-C. Edward Parker and Metro Kalimon ABSTRACT: Metal to metalbonding using a heat-sensitive adhesive is effected by application ofultrasonic energy to a metal-adhesive-metal assembly. The metals bondedmay be, for example, sheets, strips, or the ends of a can blank, thusproducing a side-seam.

METAL-METAL BONDING This invention relates to metal-metal bonding usinga heatactivatable adhesive.

In one aspect, the invention provides a method of bonding metal to metalwith a heat-activatable adhesive, which comprises forming an assembly oftwo pieces of metal to be bonded, and between them, in contact witheach, a layer of a heat-activatable adhesive for the metal or metals,and activating the adhesive by means of ultrasonic energy, while holdingthe assembly under pressure.

The invention is particularly applicable to the formation of seams, e.g.side-seams, for cans. In this application, the two pieces of metal to bebonded are the two ends of a can blank, and the assembly is formed so asto bond together the overlapping ends, thus completing the can cylinderand forming a side-seam. It will be understood therefore that the termpieces of metal" may be construed in the sense of two separate pieces ofmetal or as two separate portions of one metal body.

In one method of practicing the method of the invention, the ultrasonicenergy is transmitted through a plunger, made of solid metal or othermaterial capable of transmitting ultrasonic vibrations and resistant tohigh temperatures, while the assembly of metals and the adhesive ismaintained under pressure between the plunger and a support. The plungerface will be shaped as desired according to the shape of the metal to bebonded. In forming seams for cans the operating surface of the plunger,i.e. the surface which makes contact with the assembly, will preferablybe rectangular.

The support member may take any appropriate shape. It may be a simpleplatform. Preferably it will have a clamp or other means of securing theassembly of metals and adhesive to the support. The support bay be fixedand the plunger movable, or the plunger fixed and the support movable.Preferably the support is fixed, especially when the method is appliedto the formation of seams for cans.

Members which are capable of transmitting ultrasonic energy are known inthemselves, and normally comprise a socalled horn" of titanium or othermetal which is fastened at is broader end to a transducer element insuch a way that a node occurs at the point of junction between the hornand the transducer element, and an antinode at the tip or operatingsurface of the horn. The precise shape of the horn and its length andgeneral cross section will, of course, depend primarily on theultrasonic frequency which is to be employed, and can easily bedetermined by trail and error for any given frequency once the size andshape of the operating surface have been chosen with regard to theparticular operation to be performed. Alternatively the frequency can bechosen to suit a particular length and general cross section. Normallythe frequency will be between and 50 kc./s., preferably 18-20 kc./s.Frequencies much lower than 18 kc./s. will not usually be used, so as toavoid discomfort to the operator. Other materials of construction whichmay be employed instead of titanium include for example Duralumin, toolsteel and phosphor bronze. Titanium is preferred however as giving thelongest life.

The particular type of generator of ultrasonic energy employed is notimportant. Usually it will probable be found most convenient to use amagnetostrictive device, but other devices for generating high-frequencyvibrations such, for example, as piezo-electric devices can be employed.

It may be desirable to provide means for cooling the transducer elementand/or the plunger during operation. This may be done for example bysurrounding the transducer element with a water-bath or similar coolingmeans, and by including cooling water channels within the body of theplunger.

In a preferred method of carrying out the invention, there areinterposed, between the plunger head and the uppermost metal piece andbetween the lowermost metal piece and the support respectively, cushionmembers which transmit ultrasonic energy and are not good conductors ofheat. The cushion members may be, for example, thin metal bridges thefeet of one of which make contact with the plunger face, and the feet ofthe other with the support, i.e. one bridge is upturned with respect tothe other. The bridges are preferably thin, subject to their beingstrong enough to withstand the pressure generated between the supportand the plunger head.

If they are too thick, the heating time will be unnecessarily long asthe bridges will be better conductors of heat. Even better cushionmembers are provided by sheets of material which are less good heatconductors, especially good thermally insulating materials such aspolytetrafluoroethylene sheets. Such sheets may suitably be 0.13-0.25mm. thick, and being nonconductors, are not provided with feet or otherprojections.

The adhesive will usually be one of the many known organicheatactivatable adhesives, particularly a straight or branched chainpolyamide, e.g. Nylon ll or 12, or an ethylene/acrylic acid copolymer.They may contain one or more curing accelerators, e.g. p-quinone dioximedibenzoate.

In another aspect the invention comprises apparatus for carrying out theabove-described method, comprising a support for the assembly, anultrasonic generator, a member capable of transmitting ultrasonic energyfrom the generator to the assembly on the support, and means whereby anassembly on the support can be pressed between the support and thetransmitting member, held under pressure therebetween for apredetermined time, and then released. Suitable apparatus is illustratedsemidiagrammatically in the accompanying drawing, in which:

FIG. 1 is a diagrammatic front elevation, partly in section,

FIG. 2 and 3 are cross-sectional and side elevational views of means forsupporting a can-blank, and

FIG. 4 shows in section an assembly of two strips of metal and anintermediate adhesive layer.

Referring first to FIG. 1, the apparatus comprises a transducer 26electrically connected through wires 22, to a generator 21 andsurrounded by a water-cooled jacket 23 having an inlet 24 and outlet 25.The water-cooled jacket 23 is bolted to a mounting plate 28. A velocitytransformer 27 is secured to the bottom of the jacket 23 to lie withinthe jacket under the transducer 26. The ultrasonic probe 29 is fixed tothe bottom of the velocity transformer 27. The probe comprises a solidplunger 31 which can be dismantled from the remainder of the probe.Various types of plunger may be employed, and are preferably so mountedthat they can be quickly interchanged. The plunger 31 may, if desired,be provided with a water-cooling system 30.

Where, as in the apparatus shown in FIG. 1, the probe is fixed, theapparatus comprises means for moving the whole piece to be jointed intoand out of contact with the plunger 31. The workpiece (not shown) ismounted on a platform 32 which is attached to a column 33, which ismovable vertically into and out of a chamber 34 by any conventionalmeans, e.g. hydraulically, mechanically or electrically. The means showndiagrammatically in FIG. 1 comprises a double-action cylinder 34, a pairof pipes 35 for supplying compressed air to, and for exhausting airfrom, cylinder 34, a solenoid-actuated valve 37 for controlling the flowof compressed air, along pipes 35 from a source of compressed air (notshown), and a pipe 36 connecting said source to the valve 37.

A timing device represented diagrammatically by 39 is connected to valve37 by wires 38. It can also be connected to generator 21 by furtherwires 40.

Referring now to FIG. 4, in one method of operation, ametal-adhesive-metal assembly comprising two metal sheets 50 and anintermediate adhesive layer 51 is mounted on platform 32.Polytetrafluoroethylene sheets 0.l5 mm. thick'(not shown) are placedbetween the platform and the lowermost metal sheet and between theplunger and the uppermost metal sheet. Compressed air is fed throughvalve 37 into the lower pipe 35 and column 33 and platform 32, bringingthe assembly into contact with the face of plunger 31. Meanwhile, thetiming device 39 which actuates valve 37 trips a switch to startgenerator 21 and hence produces ultrasonic energy by means of transducer26. Alternatively the generator can run continuously or activated bymovement of the platform. The ultrasonic energy so created istransmitted through the velocity transformer 27 and the solid plunger 31to heat the adhesive. After'a predetermined time interval, valve 37 isactuated to release compressed air from cylinder 34 and thereby lowerplatform 32 to release the bonded assembly from contact with theplunger, and at the same time the current to the generator 2! isswitched off.

Referring to FIGS. 2 and 3, in another method of operation of theinvention, the support member 32 of FIG. I is replaced by a cylindricalmetal mandrel 2, which, if desired, may be coated withpolytetrafluoroethylene or other thermal insulating material. A canblank 4 is supported on the mandrel and held in place by removablearcuate ring member 3. The plunger 1 is lowered and impressed on themetal at the point of overlap to form a can side-seam.

it is a particular advantage of the invention that the aparatus isextremely compact, and only the actual areas to be bonded need beheated. A

The operation of the method may be continuous. For example, side-seamsfor cans may be formed by moving a long cylindrical mandrel supportingcan blanks beneath a transmitting member and stamping the member downonto the can blank at regular intervals. The transmitting member maycontact the whole of the seam simultaneously, or may be caused to travelalong the seam. The potential adhesive may be placed on the cans in theform of a tape or ribbon, and may be extruded directly onto themupstream of the ultrasonic heating apparatus.

The following examples illustrate the invention.

EXAMPLES 1-4 The following general method was employed in example I. Astrip of heat-sensitive adhesive 1 cm. by 1 cm., 0.13-0.25 mm. thick,was placed on one end of a piece of metal 1 cm. wide and 0.15 mm. thick.A precisely similar strip of metal was placed over the original strip sothat the amount of overlap of the two pieces of metal was 1 cm., and theadhesive lay between the two metal strips at the region of overlap.

A metal bridge 0.22 mm. thick was placed on the platform of an apparatusas described in H0. 1 of the drawing, except that the probe head was notprovided with a liquid cooling passage. The metal-adhesive-metalassembly was placed on top of the bridge. Between the uppermost sheet ofmetal, and the probe was placed an upturned metal bridge. The assemblyon the platform of the bridge-metal-adhesive-metal upturnedbridge wasbrought up we Stationary probe by an upward force of 110 kg. on theplatform, and ultrasonic energy was generated and transmitted throughthe probe. The ultrasonic energy generator was switched off after a timeshown below and the platform returned to its original position. Themetals were bonded by the adhesive, which was now 0.075-0. l 3 mm.thick. The lap-strength of the bond was tested in a tensile tester.

The same method was used in examples 2 and 3 with the modification thateach metal bridge was replaced by a 0.15 mm. thick sheet ofpolytetrafluorethylene.

Details of examples 1-3 are shown in table 1.

1. A mild steeh highly oriented, fltlfl llLlitl to prod ige a (as across-linking a ent, which also increases the viscosity of thecomposition an the strength of the bonded product) and 45 parts byweight of titanium dioxide (as a whitening agent).

The precise lap shear strengths could not be determined as the metalbroke before the joint.

EXAMPLES 4-7 The method of examples 2 and 3 was repeated except that theoverlap between the metal strips was reduced to one half Table 11shows'the operating details and the results ob- L TABLE 11 Time ofheating by ultra- Lap sonic shear energy strength Metals bonded Adhesive(sections) (kg.lcm.'-)

Example:

5 49 4 As Example 2.-. Nylon 11 1n 168. 3 63 5 As Example 3.-. AsExample 3. g 10 108 s Weirehr0me ox asza.15.---{ 3 ,3 7. Tin platedsteel- Versalon 1150. 64

a ltletal broke. a.

Key:

5. A high molecular weight solid polyamide made by General Mills.

Examples 4-7 illustrate the dependence of bond strength on the time ofheating. The optimum time for a particular metaladhesive-metalcombination can easily be determined by sim- -ple tests. The bondstrengths obtained are' very high, having gregard to the particularmetal-adhesive-metal combinations. i Even the result in example 7 isvery satisfactory as "Versalon 1140 is not a high-strength adhesive.Peel strengths were measured by bonding completely overlapped metalstrips according to the methods of example 6 with a 10 second heatingtime, and example 7 with a 5 seconds heating time. The peel strengthswere (respectively) 4.5 and 2.7 kgJcm.

The side-seams of metal cans can be formed using the above techniquesand the apparatus of FIG. 1-3 of the drawings.

We claim:

1. method of forming a metallic can cylinder which comprises applying anheat activatable adhesive to at least one end of a metallic can blank,overlapping the opposed ends of the blank to define a cylinder, andapplying pressure and ultrasonic energy in the frequency range betweenabout 15 and 50 kc./s. to the overlapped ends for a time sufficient tobond he n and thereby from a side eam having an adhesive film thicknessin the range of about 0.0754163 mm.

2. A method according to claim 1 wherein the adhesive is applied in theform of a tape.

3. A method according to claim 1 wherein the adhesive is extrudeddirectly onto one of the ends.

4. A method according to claim 1 wherein the blank is formed oftin-plated steel and the adhesive is a polyamide.

2. A method according to claim 1 wherein the adhesive is applied in theform of a tape.
 3. A method according to claim 1 wherein the adhesive isextruded directly onto one of the ends.
 4. A method according to claim 1wherein the blank is formed of tin-plated steel and the adhesive is apolyamide.